Electric delay circuit



i J 1952 R. E. COLLIS ET AL ELECTRIC DELAY CIRCUIT Filed May 13, 1948 RE. COL L IS lNl/ENTORs. J. W DEHN A T TORNE V Patented June 17, 1952 UNITED STATES PATENT OFFICE ELECTRIC DELAY CIRCUIT Application May 13, 1948, Serial Ne. 26.2%

8. Claims. 1

This invention relates to electric delay circuits, and more particularly to delay circuits in which the delay interval, may be changed after timing has been started.

In various electrical systems such as those employed. for example, in telephony, it isfrequently necessary to introduce time delay intervals between the operation of one element of the circuit and another element thereof. Many means have been devised to accomplish this result, some of the more satisfactory types utilizing the inherent delay in the charging or dischargin 01" a condenser tocontrol the time at which a'unidirectional current flow device such as a rectifier,- vacuum tube or gas-filled tube will conduct sufficient current to operate a relay. Methods have also been propounded for adjusting such delay intervals, comprising in most cases either an adjustable resistance or an adjustable capacitance.

However, the necessity arises in various applications of time delay circuits to vary the time delay interval after the timing period has started. For instance, in automatic telephone switching the interval between the time a trunk is seized and the time the trunk is used is dependent-upon the time the sender requires to forward the requisite information. A time delay circuit may be adjusted for a certain delay interval commencing atthe time'the trunk is seized, and upon the receipt of an indication from the sender that a lesser delay period is required, it is desirable to be able to reduce the interval for which the time delay circuit has been preset. In other applications it may be desirable to extend the period after the timing interval has started.

The present invention proposes circuits adapted to provide both a delay interval and means to vary that time interval after the com mencement thereof. In general, the circuits utilize'the time delay ofa resistance-capacitance network to regulate the-time at which a substantially unidirectional current flow device will be rendered suflicientl'y conductive to operate a relay orother current-sensitive control device. In each of the preferred embodiments presented herein, the unidirectional current flow device is normally biased at a certain potential, i. e., there is a certain preselected potential difierence between the main electrodes of the device. Means are provided for changing this interelectrode potential difference operable either before or after the timing period has started to either lengthen o1" shorten such period. The means 2 comprises, inthedepicted embodiments, a switch operableto either increase or decrease the biasing potential difference. between the main; electrodes, of the unidirectional current flow device, thus requiring either a lesser or greater accumulationlof charge on the condenser to cause the device to, become. sufficiently conductive to onerate a. relay. In this manner a proportionally lesser or. greater time delay interval is. obtained.

The utilization of a conventional dry rectiher, of a gaseous diode, ofa vacuum tube andof a gaseous triode as the unidirectional current flow device, and further detailsv of the. circuits will be more fully understood from the ensuing detailed, description made in reference to, the accompanying drawings in which:

Fig; 1 represents a circuit arranged in accordance with the invention in which a dry rectifier is used as the uni-directionalcurrentflow device;

Fig: 2 represents a circuit inwhich a vacuum triodeisused as such a device; and

Fig. 3' depicts an embodiment of the invention in which a. gas-filled tube is used.

Referring now to Fig. l, a source of positive potential is connected through resistor l to one side of condenser 2, the other side of which is connected to a source of negative potential. A resistance 3 shunts condenser 2 under the control of contacts 4 of start relay 5which is energized by battery 6. upon the closure of switch I. A. dry rectifier 3 of any well-known type anda relay 9 are connected between one plate oicondenser 2. and ground'through contact In of relay H which is energized by battery l2 upon the closure of switch It. The value of resistor I, is high compared to that of resistor 3', and there'- fore in the depicted unoperated' conditionof the circuit, the major portion of the potential drop occurs across resistor l. The values of the two resistances are so proportioned that at this time there is a negative potential relative to ground at point Miadjacent' the condenser 2 and thus substantially no current will flow through relay 9 since rectifier 8 is a unidirectional current flowdevice presenting a low impedance to conventional current flow therethrough in a, rightdire-ction, and presenting a high impedance to conventional current flow therethrough in left-hand directicn. Upon operation: of start relay 5' through the closure of switch 1, the shunt around condenser 2 is removed and the condenser will then commence to charge through resistor l. When the upper plate of condenser 2 reaches a potential positive relative'toground potential, rectifierB will conduct and when the upper plate of condenser 2 reaches a potential sufficiently positive relative to ground potential to cause sumcient current to flow to meet the minimum operating requirements of relay 9, relay S: will operate thereby closing contacts 55 which may control an external load circuit. This normal delay interval between the operation of relay 5 and the operation of relay 9 is proportional to the product of the resistance 1 and the capacitance 2 and therefore may be preselected by means of adjusting the value of either.

In order that this preselected delay interval may be changed after the timing period has commenced, a source of negative potential is connected through adjustable resistor 16 to the rectifier 8relay 9 series circuit at point IT. This potential normally has no effect on the operation of relay 9 inasmuch as point I! is grounded through contacts [0 of relay II. In order that the potential at point H may be adjustable by means of resistor l6, resistor I8 and ground may be connected at point H. Upon operation of biasing relay ll through the closure of switch ground is removed. A negative potential is thereby placed on the circuit at point I! and in order for the rectifier 8 to become conducting, it is only necessary for the potential on condenser 2 to be positive relative to the potential at point ll. Therefore, the condenser need not accumulate as high a charge and the timing period is thereby reduced. The extent of the reduction is of course dependent upon the parameters of the circuit, and may be adjusted by changing the value of the biasing negative potential at point I! which may be accomplished by adjusting the value of resistance [6. Conversely, if it is desired that the timing period be lengthened after the interval is started, a positive biasing potential may be applied at point H, or contacts 10 may be arranged to make upon energization of relay II and thus apply ground after timing is started. It is also apparent in the circuit of Fig. 1 that if biasing relay H is i normally operated, release of relay l l subsequent to the operation of relay 5 will lengthen the timing period.

Deenergization of relay 5 will cause contacts 4 to release to again place resistance 3 in shunt of condenser 2 to allow condenser 2 to discharge to the normal unoperated state of the circuit, and to thereby result in the release of relay 9.

It is believed to be evident that rectifier 8 might be replaced by a two-electrode gas-filled reducing or increasing the degree to which condenser 2 must be charged in order for the tube to fire, and thus accordingly reducing or increasing the timing interval as above described.

Fig. 2 represents a circuit arranged to accomplish the desired variations in time delay interval in which a vacuum tube has been utilized as the unidirectional current flow device. This vacuum tube IS has been depicted as a triode having an anode 20, a cathode 2!, and a grid 22. A source of positive potential 23 is conl3 contacts [0 break and this 4 nected to the anode 20. The cathode 2| is connected through the winding of relay 24 to ground through contacts 25 of relay 26 and also through a voltage divider comprising a source of negative potential 21, an adjustable resistor 28, resistor 23 and ground. The grid 22 of vacuum tube 19 is connected through current limiting resistor 30 to a series circuit comprising a source of negative potential 3|, a condenser 32, an adjustable resistor 33 and ground. Resistor 34 is placed in shunt of condenser 32 under the control of contacts 35 of relay 36. Under the depicted unoperated conditions, tube [9 is biased so as to be nonconducting. Upon the closure of switch 31, relay 36 will be energized by battery 35 to break contacts 35 to remove the shunt from condenser 32. The condenser will then commence to charge through resistance 33, the rate of such charging being preselectable either through adjustment of the value of con denser 32 or resistance 33. When, in the depicted embodiment, the condenser is charged to a point near ground potential, depending upon the characteristics of tube l9, tube 19 will conduct current through its output circuit including anode 20, cathode 2|, relay 24, contacts 25, ground and to battery 23. Relay 24 will then operate to close contacts 39 to control an external load circuit.

In order to reduce the preselected time delay after the interval has commenced, switch 40 may be closed to cause battery 4! to energize relay to thereby open contact 25 and remove the ground from the circuit. The potential then applied to the cathode of tube I 9 will then be more negative than ground and condenser 32 will have to charge to a lesser degree than previously to build up a sufiicient potential on grid 22 to render the tube conducting. A lesser delay interval will thus result.

The reduction in the delay between the time at which relay 36 is operated until relay 24 will operate, may be changed by adjusting resistance 23. As was discussed in regard to Fig. l, the timing period may be lengthened after the interval has been commenced either by having relay 26 normally operated and releasing it to increase the timing interval, or by providing relay 26 with make rather than break contacts, or by providing a source of positive potential 27 rather than the depicted negative soiu'ce. Other modifications will be obvious to those skilled in the art.

Release of relay 36 will replace the shunt around condenser 32 which will discharge through resistance 34, and the circuits will return to their unoperated condition releasing relay 24.

Fig. 3 represents a circuit arranged to provide a variable time delay interval in which a gasfilled triode has been utilized as the unidirectional current flow device. The depicted doublegap cold-cathode gas-filled tube 42 is provided with an anode 43, a cathode 44 and a starter electrode 45, though it is to be understood that a gas tube of the thyratron or other type may be used. A source of positive potential 46 is connected to anode 43. When relay 48 is unoperated, the oathode 44 is connected through back contacts 4'! of relay 48, through resistor 49 and to ground. This resistor 49 and the ground potential are provided to stabilize the potential at the cathode to prevent stray capacitance or stray leakage from causing the cathode potential to vary. Cathode 44 is con nectable, by means of front contacts 50 of relay 48, "through the winding of relay 5! to ground through contacts 52 of relay 53. The cathode is also connected through contacts 50 of relay 48, winding of relay 5|, and to a voltage divider comprising a source of negative potential 54, an adjustable resistor 55, resistor '56 and to ground.

Starter electrode of gas tube 42 is connected through current limiting resistor 5-! to a series circuit comprising a source of positive potential 58, adjustable resistor 59, condenser 60 and ground. Resistor 6| is placed in shunt of condenser it under control of contacts 62 of relay 48'. Under the depicted unoperated condition, tube '42 is biased so as to be non-conducting. Upon the closure of switch 63, battery 64 will energize start relay 4B which will break contacts 62 to remove the shunt from condenser 66, and will also transfer the cathode lead from contacts 4'! to contacts 50 to place a potential on the cathode substantially equal to ground. tial on the tube at this time is such that there will be a certain delay interval before condenser will have attained a sufficient charge to apply the requisite potential on starter electrode 45 to cause tube 52 to fire. With a tube of given char- 1i acteristics, this period may be preset by the adjustment of either condenser it or resistance 59. When tube 42 becomes conductive, current will flow through the output circuit of that tube to The bias potenoperate relay 5! thus closing contacts to con-- :jfl

trol an external load circuit.

To vary the timing interval after timing has started, the bias potential may be shifted, a shift increasing the potential difference across the main gap of the tube shortening the timing period, and, conversely, a shift decreasing the po tential difference across the main gap lengthening the timing period. This is accomplished in the circuit of Fig. 3 in much the same manner as that described in relation to the circuits of Figs. 1 t

and 2. Upon the closure of switch lit, battery 5 will energize relay 53 to break contacts 52 and thus remove the ground. A potential more negative than ground will then be placed on cathode 54 thereby shifting the bias on tube 42 so that it will fire with a lesser potential on control elsetrode 45 and thus will be rendered conductive more rapidly. Resistance '55 may be adiusted to vary this decreased interval, and, as before described, positive battery may be substituted at 54, or relay contacts 52 may be modified to the period of delay to be lengthened.

In order to extinguish gas-filled tubes, it is necessary to reduce the potential difference between the anode and cathode to a point below the sustaining voltage thereof. Therefore, in the clrcuit of Fig. 3, upon the release of start relay 48 not only is the shunting resistance 6! replaced around condenser 60, but also contacts 59 are broken to cause the tube 42 to extinguish and the relay 5| to release. It is to be understood, however, that any other well-known means of reducing the anode potential to extinguish the tube may be used.

It will be noted that in each of the depicted circuits, if a sufficient interval has elapsed before the biasing relay is operated, operation of the biasing relay will cause the unidirectional current flow device to conduct practically instantaneously. For instance, if the parameters of the circuits be such that with the biasing relay unoperated, 0.8 second will elapse between the operation of the start relay and the operation of the circuit control relay, and with the biasing relay operated there will be but, for example, a

tive batteries, negative 130 volts.

0.4 second delay, operation of the biasing'relay after 0.4- second has elapsed, but before the 111111 0. 8 second has expired, will cause the unidirectional current flow device to operate immediately.

Although it is to be understood that the following parameters are purely exemplary and may be varied to "meet the requirements of any particular embodiment of the invention, the various elements of the several depicted systems may be of the following values: Fig. 1: resistor I, 10,000 ohms; capacitor 2, 10 microiarads; resistor 3, ohms; resistor it, 800 ohms; resistor 18, 200 ohms; positive battery, positive volts; nega- Fig. 2: tube type 6L6; resistor 38, 0.1 megohm; resistor 33, l megohm; capacitor 32, 10 microfarads; resistor 34, 1 000 ohms; resistors 28 and 29, 300 ohms; positive battery, positive 130 volts; negative battery, negative 100 volts. Fig. 3: tube type 313-CA; resistor 52', 0.1 'm-egohm; resistor 59, 1 megohni; capacitor Bil, l microfarad; resistor SI, 1000 ohms; resistor 4-9, 10 megohms; resistor 55, 2200 ohms; resistor 5t, 4250 ohms; positive battery, positive 130 volts; negative battery, negative 48 volts.

It will be observed that the values of the resistance-capacitance network in each case may be varied to provide any desired time constant.

Modification of the above-described circuits may also be made within the scope of the invention to provide the same results with alternating current, using half-wave rectification. and placing a filter around the winding of the load controlling relay.

It is to be understood that the above depicted and described circuits are but representative of the invention and are not to be interpreted in a limitingsensesinee many possible modifications of the circuit may be made within the scope of the appended claims.

What is claimed is:

1. In a time delay circuit, a dry rectifier having an anode and a cathode, a switch, a first source of potential connected to the cathode of said rectifier through said switch, a resistor, a second source of potential negative relative to said first potential connected to the cathode of said rectifier through said resistor, a series circuit comprising a third source of potential positive relative to said first and said second sources. a second resistor, a capacitor, and a fourth source of potential negative relative to said first source, a connection between the anode of said rectifier and said series circuit at a point between said I second resistor and said capacitor, means for operating said switch, and means operative in response to current flow through said rectifier.

2. A time delay apparatus comprising a condenser, a resistor, a charging circuit for said condenser including said resistor, a unidirectional current conducting device having two terminals, means connecting one of said terminals to a point in said charging circuit intermediate said resistor and said condenser, a load device, means for applying a biasing potential through said load device to the other terminal of said unidirectional current conducting device, a voltage source, and a normally closed switch connecting said voltage source to said other terminal of said unidirectional current conducting device through said load device.

3. A time delay apparatus comprising a condenser, a resistor, a charging circuit for said condenser including said resistor and means for connecting said resistor and said condenser in series, a unidirectional current conducting device having two terminals, means connecting one of said terminals to a point in said charging circuit intermediate said resistor and said condenser, a load device, means for applying a biasing potential through load device to the other terminal of said unidirectional current conducting device, a voltage source, a normally closed switch connecting said voltage source to said other terminal of said unidirectional current conducting device through said load device, and means for opening said switch.

f1. A time delay apparatus comprising a switch, a condenser, a resistor, a charging circuit for said condenser controlled by said switch including said resistor, a unidirectional current conducting device having two terminals, means connecting one of said terminals to a point at said charging circuit intermediate said resistor and said condenser, a load device, means for applying a biasing potential through said load device to the other terminal of said unidirectional current conducting device, a voltage source, a normally closed switch connecting said voltage source to said other terminal of said unidirectional current conducting device through said load device, and means for opening said normally closed switch.

5. A time delay apparatus comprising a unidirectional current conducting device and a load connected in series therewith, means for applying an initial voltage to one side of said device, means for slowly increasing said initial voltage comprising a condenser, a resistor and a charging circuit for said condenser including said resistor, a normally closed switch, means including said switch for applying another initial voltage to the other side of said device through said load, and means for applying a different voltage to the said other side of said device comprising a voltage source connected to said other side of said device through said load and means for opening said switch.

6. A time delay apparatus comprising a unidirectional current conducting device and a load connected in series therewith, means for applying a first initial voltage to one side of said device, a normally closed switch, means including said normally closed switch for applying a second initial voltage to the other side of said device 5 through said load for initially biasing said device non-conducting, means for slowly increasing said first initial voltage for rendering said device conductive after a delay interval comprising a condenser, a resistor and a charging circuit for said condenser including said resistor, and means for changing said second initial voltage comprising a voltage source connected to said other side of said 8 device through said load and means for opening said switch.

7. A time delay apparatus comprising a unidirectional current conducting device and a load connected in series therewith, means for applying a first initial voltage to one side of said device, a normally closed switch, means including said normally closed switch for applying a second initial voltage to the other side of said device through said load for initially biasing said device non-conducting, means for slowly increasing said first initial voltage for rendering said device conductive after a delay interval comprising a condenser, a resistor in series with said condenser and a charging circuit for said condenser including said resistor, and means for changing said second initial voltage comprising a voltage source connected to said other side of said device through said load and means for opening said switch.

8. A time delay apparatus comprising a unidirectional current conducting device and a load connected in series therewith, means for applying a negative initial voltage to one side of said device, a normally closed switch, means including said normally closed switch for applying an initial voltage of ground to the other side of said device through said load for initially biasing said device non-conducting, means for slowly increasing said negative initial voltage to a positive value for rendering said device conductive after a delay interval comprising a condenser, a resistor in series with said condenser, and a charging circuit for said condenser including said resister, and means for changing said ground initial voltage for varying said delay interval comprising a source of voltage other than ground and a resistor serially connected to said other side of said device through said load and means for: opening said switch.

RAYMOND E. COLLIS. JOSEPH W. DEHN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,762,811 Charlton June 10, 1930 1,917,418 Almquist July 11, 1933 2,040,425 Biach May 12, 1936 2,114,016 Dimond Apr. 12, 1938 2,360,721 Rose Oct. 17, 1944 2,370,727 Holden Mar. 6, 1945 2,372,005 Kinsman Mar. 20, 1945 2,445,051 Wilson July 13, 194R 

